1. Technical Field
The disclosure generally relates to the field of multi-standard wireless communication systems and especially to communication terminals applicable for different broadcast and communication standards. These communication terminals are further referred to as multi-standard wireless communication terminals.
2. Description of the Related Art
In recent years different wireless communication standards such as Universal Mobile Telecommunications Systems (UMTS), General System for Mobile Communications (GSM), Wireless Local Area Network (WLAN), Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and Bluetooth have been developed for various wireless communication applications.
To use communication services supported by at least two different communication standards so-called multi-standard wireless communication terminals have been developed supporting at least two different air interfaces. In many cases, these multi-standard wireless communication terminals support multi-system operations, e.g. they are capable of transmitting voice or data on different supported wireless communication standards. Sometimes, even multi-standard handovers, e.g. a transition between the systems during a call, are supported, for example between GSM and WLAN.
Such a multi-standard wireless communication terminal consists of a variety of different terminal communication systems, each supporting a specific broadcast (“one-way”) and/or communication (“two-way”) standard. Said different terminal communication systems of a multi-standard wireless communication terminal may have their own reference clock unit to produce an own reference clock signal. Having a variety of different communication units in a single terminal communication system, it is always desirable to share as much as possible units and components. Therefore, preferably a common reference clock unit may be shared by all terminal communication systems within a multi-standard wireless communication terminal producing one common reference clock signal. While having a common reference clock unit, a unified automatic frequency control (AFC) is used.
From US 2004/0037379 A1 a multi-standard radio communication terminal is known, using a shared clock source for providing simultaneous time base monitoring for GSM/TDMA/EDGE using accumulator type layer 1 timers.
WO 2005/069661 A1 describes a method of synchronizing a first and a second time base unit in a multi-standard receiving station consisting of several time base units to provide different clock signals for the supported transmission standards, wherein one of said time base units acts as a “master” time base unit. Said “master” time base unit is calibrated and the calibration datum is reused for the calibration and synchronization of the remaining time base units.
WO 02/104050 A1 discloses a method for synchronizing a multi-standard base station using one clock, wherein the system to be synchronized are GSM- or EDGE-type telecommunication systems. The clock of the WCDMA-type system is selected as the system clock of the multi-standard base station and the clock of the GSM-type system is using multiples of the frequency of the selected clock. One clock again acts as a master clock for both systems.
Said architectures according to the state of the art use a master system, having a continuously working clock control, which is typically not the case for TDMA-standards like GSM, IS136 etc. Furthermore, said architectures are not suited for low cost and low power multi-standard wireless communication terminals, as each terminal communication system uses its own reference clock unit increasing the size of the electronic design as well as the design costs and power consumption of the design.
FIG. 1 shows per way of example a block diagram of an architecture of a multi-standard wireless communication system WTS according to the state of the art consisting of several radio communication systems RCS1-RCSn.
Each of said radio communication systems RCS1-RCSn enables at least a data broadcast from a counterpart communication station CCS1-CCSn, located upstream of each radio link RL1-RLn, via at least one radio link RL1-RLn to a multi-standard wireless communication terminal located downstream of each radio link RL1-RLn and including several terminal communication stations CS1-CSn. In addition to said downstream communication, also an upstream data communication between said terminal communication stations CS1-CSn and at least one counterpart communication station CCS1-CCSn can be provided. The radio link RL1-RLn is established between an antenna A1-An connected to said terminal communication stations CS1, CS2-CSn and a counterpart antenna CA1-CAn attached to said counterpart communication stations CCS1, CCS2-CCSn.
Each terminal communication station CS1, CS2-CSn includes a signal generation unit SGU1-SGUn, a signal conversion unit SCU1-SCUn, a reference clock unit RCU1-RCUn and a clock control unit CCU1-CCUn. The signal generation unit SGU1-SGUn is attached to the signal conversion unit SCU1-SCUn, which is connected to said antenna A1-An as well as to said clock control unit CCU1-CCUn. Furthermore, the reference clock unit RCU1-RCUn is associated with the signal generation unit SGU1-SGUn and the clock control unit CCU1-CCUn.
In conventional architectures said signal generation unit SGU1-SGUn is a phase locked loop (PLL) circuit that includes for example a phase-frequency-detector, a loop-filter, a voltage-controlled-oscillator and a conversion ratio unit CRU1-CRUn, which may be realized by a integer divider unit, a frac-N divider unit or a divider unit working according to a further division technique. Furthermore said signal generation unit SGU1-SGUn maybe realized as a “direct-digital-synthesis” (DDS) system.
The frequency synthesis done by said signal generation unit SGU1-SGUn is based on a reference clock signal rcs1-rcsn provided by the reference clock unit RCU1-RCUn. Each signal generation unit SGU1-SGUn generates a conversion signal cs1-csn that is supplied to the attached signal conversion unit SCU1-SCUn, which may be realized by a mixer unit often accompanied by a low noise amplifier unit (not shown in the figures).
This signal conversion unit SCU1-SCUn is connected to the antenna A1-An for the transmission of at least one transmission signal ts1-tsn via said radio link RL1-RLn to the counterpart communication stations CCS1-CCSn. The transmission signal ts1-tsn is received by the counterpart antenna CA1-CAn of said counterpart communication station CCS1-CCSn. In addition to that a counterpart transmission signal ts1′-tsn′ is transmitted from the counterpart communication stations CCS1-CCSn to the terminal communication stations CS1-CSn comprising an accurate frequency datum ac1-acn via the radio link RL1-RLn. The accurate frequency datum ac1-acn contained in said counterpart transmission signal ts1′-tsn′ is received by the signal conversion unit SCU1-SCUn and converted in the baseband frequency domain. Subsequently the converted accurate frequency datum ac1-acn is provided to the clock control unit CCU1-CCUn.
Depending on the reference clock signal rcs1-rcsn provided by the reference clock unit RCU1-RCUn to the clock control unit CCU1-CCUn, the frequency error/frequency offset of the reference clock signal rcs1-rcsn is determined by analyzing the accurate frequency datum ac1-acn provided by the counterpart communication station CCS1-CCSn and received via said counterpart transmission signal ts1′-tsn′. Based on the analysis of said accurate frequency datum ac1-acn with respect to the reference clock signal rcs1-rcsn a frequency-error control signal fec1-fecn is generated by the clock control unit CCU1-CCUn, which is fed to the reference clock unit RCU1-RCUn to control the frequency of the reference clock signal rcs1-rcsn in order to minimize the calculated frequency error. The connection between each reference clock unit RCU1-RCUn and the attached clock control unit CCU1-CCUn is realized as a simple digital clock unit or/and a local reference signal which is used for frequency comparison with said accurate frequency datum ac1-acn.
FIG. 2 shows a further prior art architecture of a different multi-standard wireless communication system WTS utilizing, instead of one reference clock unit RCU1-RCUn per terminal communication system CS1-CSn, one common reference clock unit RCU for all terminal communication systems CS1-CSn, that is controlled by one of the terminal communication systems CS1-CSn via a single clock control unit CCU. Said common reference clock unit RCU originates a common reference signal rcs, which is provided to each terminal communication system CS1-CSn, wherein said common reference clock unit RCU maybe integrated in one of said radio communication system RCS1-RCSn or may be realized as an external unit.
Via the single clock control unit CCU a common frequency error control signal cfec is created and supplied to the common reference clock unit RCU. According to FIG. 2, said common reference clock unit RCU is per way of example attached to the first terminal communication station CS1, which comprises the common clock control unit CCU as well.
So, contrary to the system architecture depicted in FIG. 1, the further terminal communication stations CS2-CSn according to FIG. 2 comprise neither an own reference clock unit CRU2-CRUn nor an own clock control unit CCU2-CCUn. If the radio link RL1 associated with the first terminal communication station CS1 comprising the common clock control unit CCU is unstable or doesn't have a high accuracy, the whole radio communication within the multi-standard wireless communication system WTS might fail due to the still existing frequency error.